Moment method analysis of mutual interaction in MRI phased array coils

We describe the use of a computational method for determining the overlap distance minimizing the mutual interaction between two adjacent coils that constitute a part of a phased array system used in MRI. The method is based upon the method of moments, and the analysis is carried out at a target imaging frequency to obtain the overlap distance. For a variety of complex RF phased array coils, we can determine, using the proposed approach, the overlap distance between nearest neighbor block element RF coils such that the mutual interaction is nullified or minimized. We give experimental results to validate the proposed approach. When compared with the experimental data, our theoretical prediction is in excellent agreement.     

Current waveform control of a high‐power‐factor rectifier circuit for harmonic suppression of voltage and current in a distribution system

This paper presents the input current waveform control of the rectifier circuit which realizes simultaneously the high input power factor and the harmonics suppression of the receiving‐end voltage and the source current under the distorted receiving‐end voltage. The proposed input current waveform includes the harmonic components which are in phase with the receiving‐end voltage harmonics. The control parameter in the proposed waveform is designed by examining the characteristics of both the harmonic suppression effect in the distribution system and the input power factor of the rectifier circuit. The effectiveness of the proposed current waveform has been confirmed experimentally. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(4): 62–71, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10046     

Synthesis of polymer/1T-TaS2 layered nanocomposites

Single-phase layered nanocomposites containing 1T-TaS₂ and poly(ethylene oxide) or poly(ethylenimine) have been first synthesized by using the exfoliation-adsorption method. They have been characterized by powder X-ray diffraction. As the products exhibited lattice expansions along the stacking direction, poly(ethylene oxide) and poly(ethylenimine) were intercalated into 1T-TaS₂ galleries. Despite high conductivity of the host material, the resistivities of the polymer/1T-TaS₂ nanocomposites were found to be high in the order of 5.9-13 Ω cm.     

A two‐layered neighborhood tabu search‐based approach to optimal allocation of D‐FACTS in distribution systems

This paper proposes two‐layered neighborhood tabu search for determining the optimal allocation and output of D‐FACTS device in a distribution system with uncertain wind power generation. In recent years, wind power generation has been introduced into distribution systems for clean and inexhaustible distributed generation. However, a distribution system with wind power generation often encounters the reverse flow due to the uncertain output performance of wind power generation. As a result, the voltage variation may become much larger. In this paper, two‐layered neighborhood tabu search is proposed to determine the optimal allocation and output of D‐FACTS devices. To consider the uncertainty of wind power generation, this paper carries out Monte Carlo simulation to evaluate the probabilistic voltage assessment in the distribution system with uncertain wind power generation. The proposed method is successfully applied to a sample system. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 29–37, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20103     

Kinetics of trichloroethene dechlorination with iron powder

The dechlorination of trichloroethene (TCE) with metallic iron is an advantageous method for the remediation of contaminated groundwater and soil. The toxic reaction intermediates such as dichloroethenes (DCEs) and vinyl chloride (VC), however, occasionally accumulate in the pathway of the reaction. We have been trying to suppress these intermediates by using metallic iron powder containing impurities. In order to investigate the reaction pathways, we measured the production rates of the intermediates and the final products of the dechlorination of TCE such as DCEs, VC, ethyne or ethene. Ethyne, ethene, ethane and cis-DCE were observed as the major products, and trans-DCE, 1,1-DCE, VC, C3-hydrocarbons (such as propane, propylene), C4-hydrocarbons (such as n-butane) and methane were observed as the minors. Also the rate constants of TCE to ethyne and ethyne to ethene were larger than any other constants. These fact show the production of ethene/ethane via ethyne is the main pathway of the dechlorination of TCE using the metallic iron powder.     

Determination of organotin compounds in polyvinyl chloride toys

Organotin compounds in polyvinyl chloride toys were determined by GC/MS after ethyl derivatization with sodium tetraethylborate. The samples were 12 balls, 12 soft toys, 10 food toys and 13 face masks for children. Monooctyltin, dioctyltin and trioctyltin compounds were found in all face masks at the levels of 74.8-917 micrograms/g. 474-3,960 micrograms/g and 1.0-213 micrograms/g, respectively. They also were detected in 6 balls, 4 soft toys and 1 food toy. Monomethyltin and dimethyltin compounds were found in 8 face masks at the levels of 40.9-227 micrograms/g and 222-1,450 micrograms/g, respectively. Monobutyltin and dibutyltin (DBT) compounds were found in 1 ball, 3 food toys and 5 face masks. In particular, 1 ball and 4 face masks contained toxic DBT at the levels of 527-999 micrograms/g.     

Thermal conductivities of molten iron, cobalt, and nickel by laser flash method

New attempts were made for the measurement of thermal diffusivity of molten iron, cobalt, and nickel at temperatures close to 1900 K by a laser flash method. A simple but useful sample cell system was developed to keep the molten metal shape uniform for a given thickness. It is also necessary to consider the effect of not only the radiative heat loss but also the conductive heat loss at the interface between the molten metal sample and the sample cell material under the present experimental conditions. The conductive heat loss was found, through computational simulation, to be negligibly small for the present laser flash measurements. Thermal conductivity values of molten iron, cobalt, and nickel were calculated by combining the present thermal diffusivity data with specific heat and density, and the resulting values are given in the following equations (unit: W m⁻¹ K⁻¹)

Color segmentation for text extraction

The capability of extracting and recognizing characters printed in color documents will widen immensely the applications of OCR systems. This paper describes a new method of color segmentation to extract character areas from a color document. At first glance, the characters seem to be printed in a single color, but actual measurements reveal that the color image has a distribution of components. Compared with clustering algorithms, our method prevents oversegmentation and fusion with the background while maintaining real-time usability. It extracts the representative colors based on a histogram analysis of the color space. Our method also contains a selective local color averaging technique that removes the problem of mesh noise on high-resolution color images.Received: 25 July 2003, Revised: 10 August 2003, Published online: 6 February 2004Correspondence to: Hiroyuki Hase. Current address: 3-9-1 Bunkyo, Fukui-shi 910-8507, Japan